We understand that pilot fish are often found in schools near sharks. Why don't the sharks eat these fish? Is there some mutual benefit for them?

From:

http://www.everything2.com/index.pl?node=Pilot%20fish

"For a while, many studiers of marine life thought that pilot fish helped to lead sharks to prey (thus the name pilot fish) but after much study this appears not to be the case. Rather than having a symbiotic relationship with the sharks, as remoras do, pilot fish appear to just be along for the free food. The only reason sharks tend not to eat pilot fish is because the fish have quick enough reflexes to dart out of the way before a shark can bite it. Sharks seem to put up with pilot fish, for the most, unless there are a large number following them around."